Hi meanindya,
The basic principle to weight gain is simple: You need to consume more calories than you expend.
Follow these tips for a healthy weight gain:
1. It takes time to increase muscle weight.
2. Choose higher calorie foods from all the groups in the Food Guide Pyramid.
3. Eat larger food portions.
4. Eat five or more meals a day.
5. Drink plenty of fluids that supply calories like juice, milk, milkshakes, and sports beverages.
6. Set realistic goals.
I hope some of this helps.
Health, Safety and Financial Freedom For All -- Consumer Freedom Alliance
Smart Consumer Tips